Ignition timing advance mechanism



April 29, 1958 w. E. ARMSTRONG IGNITION TIMING ADVANCE MECHANISM 2Sheets-She Filed April 1954 lNVENTOR ATTORNEY April 29, 1958 w. E.ARMSTRONG 2,832,855

IGNITION TIMING ADVANCE MECHANISM Filed April 9, 1954 A 2 Sheets-Sheet 2INVENTOR ATTORNEY United States Patent 2,832,855 IGNITION TIMING ADVANCEMECHANISM Werner E. Armstrong, Milwaukee, Wis., assignor, by

mesne assignments, to Fairbanks, Morse & Co., a corporation of IllinoisApplication April 9, 1954, Serial No. 422,003 9 Claims. (Cl. 200-31)This invention relates to electrical jump-spark ignition apparatus forinternal combustion engines in which the combustion charge is ignitedelectrically at a position of angular advance with respect to deadcenter and it resides in novel means by which the position of advance isrendered dependent upon engine speed through a crankshaftdriven camfrictionally engaged by a contact controlling follower or wiper the cambeing capable of relative angular motion with respect to the crank andbeing urged toward an advanced relation with respect to the crank bycentrifugal means, and being urged toward retarded relation with respectto the crankshaft mainly by the frictional engagement between the wiperand cam.

The improvement of this invention is adapted for use, generally, withjump spark ignition internal combustion engines, but itschief andimportant advantages of marked simplicity and economy and its unusualcompactness render it especially useful in connection with smallportable prime movers employed to power portable tools such as lawnmowers, portable chain saws, garden tractors, washing machines andsimilar tools and appliances. In all such equipment, ease of starting,freedom from back firing, regular running at idling speeds and goodpower output at normal operating speeds are all important and desirablecharacteristics.

As is well-known, in jump-spark ignition engines, it is necessary atstarting and during idling that a retarded ignition angle of advance,not greatly in advance of top dead center, be maintained, but as enginespeed increases it is necessary that a greater ignition advance beprovided if power output is to be sustained. Means for manuallyadvancing and retarding the spark are not entirely suited to smallhigh-speed engines; and accordingly large numbers of such engines aremade and used, in spite of the disadvantages thereof, which operate witha fixed angle of ignition advance.

Means for automatically advancing the spark with increasing engine speedhave long been available for use in larger engines. A common structureof this type has included a breaker cam which is movable angularly withrespect to the crankshaft, the motion being controlled by centrifugalfly weights acting against a spring. The governor power required to moveand maintain the cam reliably against the friction imposed by thebreaker arm in such devices is considerable and for this reason flyweights of considerable mass, working against a spring of considerabletension, have been required. The minimum practical dimensions and thecost of such equipment are such as to render the use thereof, on smallengines, undesirable. In the case of small engines, advance of the sparkin strict proportion to engine speed has, in accordance with thisinvention, been found to be of minor importance, since a single retardedspark position will give good starting and steady idlingcharacteristics, free of backfiring, and a single advanced sparkposition, brought about at speeds in the lower ranges of normaloperating speed, is adequate. This is particularly true in the manyinstances where the engine is used essentially as a constant speed primemover.

It is an object of this invention to provide spark ignition meanssufliciently compact to be suitable for use in small spark ignitioninternal combustion engines, which means deliver an advanced spark atspeeds above starting and 2,832,855 Patented Apr. 29, 1958 idlingspeeds, and a retarded spark at starting and idling speeds.

Another object of this invention is to provide a speedresponsiveignition-advance for internal combustion engines, through means lowenough in cost to render the use thereof economical in prime movers ofsmall size.

It is a further object of this invention to provide centriiignailyresponsive spark advancing and retarding means for the ignition systemof an internal combustion engine which is free of dependence upon meansinterposing a continually acting force in opposition to thecentrifugally created force of the fly weight means so that the entireavailable force of the fly weight means is available to cause sparkadvance to occur, thus reducing the mass and dimensions of fly weightmeans required to produce the advancing action.

Another object is to provide a spark advance means,

, wherein the force acting to cause retarding motion, at

lower speeds, is provided by friction rather than by a spring or otherbiasing force which is continuous in its action.

These and other objects and advantages will appear from the descriptionfollowing in which reference is made to the accompanying drawings whichform a part hereof, and in which there is shown, by way of illustrationand not of limitation, a specific form in which the invention may beembodied.

in the drawings:

Fig. 1 is a side view in elevation and in section of a conventionalizedsingle cylinder two cycle gasoline engine including an improved magnetoconstructed in accordance with this invention,

Fig. 2 is a view in section of the magneto assembly of the engine shownin Fig. 1 viewed through the plane 2-2.

Fig. 3 is an exploded view in perspective of the improved advancingmechanism controlling the breaker cam of the magneto shown,

Fig. 4 is a fragmentary view of a portion of the engine crankshaftshowing the breaker cam and timing advance elements appearing in Fig. 3mounted thereon,

Fig. 5 is a fragmentary view of the crankshaft of the engine shown,viewed through the plane 55, shown in Fig. 4,

Fig. 6 is a view in cross section of the engine crankshaft showing thebreaker cam mounted thereon in retarded position together with thebreaker arm, and

Fig. '7 is another view in cross section of the engine crankshaft withthe breaker cam advanced from the position shown in Fig. 6.

The form of the invention appearing in the drawin is shown applied to amagneto ignition system for otherwise conventional, single-cylinder,air-cooled, in cycle internal combustion engine, being typical ofengines wherein the invention demonstrates its greatest utility. is tobe understood, however, that the invention may be found useful in singleor multiple cylinder engines of both the two-cycle and the four-cycletype, with either magneto or battery ignition systems.

The engine, as shown, includes a finned cylinder 1. with a central sparkplug 2 connected by a lead 3 with high tension terminal of a magnetocoil 4 housed the magneto assembly S. The cylinder 1 i secui J acrankcase 6, having bearings 7 and 8 straddling the throw 9 of acrankshaft ill rotatably mounted on the earings. A connecting rod l2.makes journaled connection at its lower end with crank pin ill, of throw9, and pivotally engages wrist pin 13 in piston 14 all in conventionalmanner. A transfer passage joining the crankcase 6 with space above thepiston, but not shown, provides an inlet for fuel and air while exhaustis through exhaust port 15. A carer. eter re, connected through aninduction valve 17 with the crankcase 6, supplies the fuel-air mixturewhich is transferred from the crankcase 6 to the cylinder 1 by crankcasecompression.

The magneto assembly 5 is provided with an inner housing 18, joined tothe crankcase 6' by brackets 19, which rigidly maintain the housing 18in concentric relation with the crankshaft 10. An extension 20 on thecrankshaft it enters the housing 18 to drive a cam 21 which acts toseparate contacts 22 and 23 joined in short circuit relationship with alow tension winding in coil 4 in accordance with customary magnetopractice.

Coil 4 surrounds a central pole 24 of a yoke 26 provided with flankingpoles 25 and 27. Yoke 26 is secured by screws 28-48 to the inner housing13 with the faces of poles 24, 25 and 27 concentric with crankshaft it}.

Separation of the contacts 22 and 23 by the cam 21 is effected throughan insulating breaker arm 29, pivotally mounted on post 31), carryingthe contact 23 and spring urged by spring 31 toward a position in whichthe contact are engaged. The end of the breaker arm 2%, opposite thatcarrying. the contact 23, extends radially inwardly with respect to theextension 20 of shaft 10 to engage the surface of cam 21 as a wiper orcam follower 32.

Cam 21 is circularly cylindrical over approximately twothirds of itscircumference while the remainder is out below the circular contour toprovide a gradual drop, into which the wiper 32 descends, to permitcontacts 22 and 23 to engage, whenever the cam 21 reaches the positionshown in Figs. 2, 6 and 7. After a short dwell in engagement, furtherrotation of cam 21 thereafter brings the gradually increasing radius ofits contour again into contact with wiper 32 producing separation ofcontacts 22 and 23. The moment of this separation creates an impulsecausing firing to occur in accordance with wellknown principles ofmagneto construction.

Secured to the extension 2d of the crankshaft 19 is a bellshapedflywheel 33 drawn to the shape shown,

serving not only as a flywheel but also to complete the enclosure of theremaining magneto parts. The flywheel 33 is formed of magnetic materialand carries strongly, permanently, magnetized rotor shoes 34 and 35,located to pass close to the pole tips of poles 25,- 24 and 27. As shoe34 leaves and shoe 35 approaches a position adjacent pole 24 a rapidlychanging magnetizing force is applied to pole 24 tending to induce arapid change in flux threading coil 4. For an interval just preceding,the primary circuit of coil 4 remains closed by engagement of contacts22 and 23, which reopens at or near a condition of maximum rate ofchange of magnetizing force.

The fixed end of spring 31 is carried in an insulated binding post 36and joined through lead 37 with the primary winding of coil 4. Theopposite end of the primary winding is electrically joined or groundedto the inner housing 18 which through bracket 38 is in electricalengagement with contact 22 supported thereon. Closure of the primarycircuit, heretofore mentioned, is thus effected upon engagement ofcontacts 22 and 23. Connected also to post 36 by lead 39, is acapacitor. 4% the opposite terminal of which is grounded through itsmounting 41 to the inner housing 18. Upon separation of contacts 22 and23 the usual oscillating discharge is caused to occur in the primarycircuit of which capacitor 48 forms a part in accordance with well-knownignition circuit practices.

Cam 21, as appears more clearly in Fig. 3, has a smooth central borewithin which the crankshaft extension 20 is received with a close butfree turning fit. Because of this freedom of motion between the cam 21and the shaft extension 20 means are provided for driving the cam. Forthis purpose, a split collar having a fixed portion 42 and acentrifugally responsive or fly weight portion 43 are assembled aboutthe extension 20 adjacent the cam 21. A key 44 received in a key slot inthe extension 20 and there rigidly held by the hub of the fly-wheel 33and nut 45 is secured rigidly to the fixed portion 42 of the splitcollar thus causing the latter to rotate with and in rigidly fixedrelation to the shaft extension 20. In this manner there is provided amounting, fixed in relation to shaft extension 20, for a pivot pin 46which in turn provides a pivotal connection between the fixed portionand the fiy weight portion of the split collar.

An actuating pin 47 extending axially from the end surface of cam 21enters, with a loose fit, a hole in the free end of the fly weightmember 43 and continuing beyond passes through a guiding and retainingslot 48 in the adjacent end of the fixed portion 42 of the split Byreason of this construction, the cam 21, the shaf extension 20 and thefly weight 43 are free to occupy and move between the two positionsshown in Figs. 6 and 7 in response to the dominating component of theresolved forces acting thereon.

As a convenient means for retaining the cam 21 against endwise movementthe key 44 is notched as at 49 to conform with or to fall below thecircumference of the shaft extension 20 thus leaving shoulders 50 and 51acting with a free sliding fit upon the end surfaces of cam 21. Asappears in Fig. 2, a lubricator felt is mounted to bear upon the camsurface of cam 21 with very little friction to maintain lubrication atthe sliding engagement between the cam 21 and the wiper 32.

It will be observed that the fly weight 43 acts against no governorspring, nor any other biasing force, acting continuously thereon, and,as a result, whenever the rate of rotation of the shaft extension 20exceeds that at which centrifugal force exceeds the retarding effect ofthe friction of wiper 32 and lubricator felt 52, cam 21 will be advancedto'the position shown in Fig. 7, and will remain in said advancedposition until speed again drops below the said determining speed. Thedetermining speed of advancing and retarding motion, herein calleddetermining speed of advance, is established by the mass of fly weight43, the mechanical advantage of the connection of the same with the cam21, and the torque imposed by parts in frictional engagement with thecam 21. Since the latter forces are comparatively constant while thecentrifugal force increases exponentially with speed, the determiningspeed of advance will occur reliably within a relatively narrow range inspite of alterations due to normal wear. 7

The scope of advance provided in the apparatus, shown in the drawings,is approximately fifteen degrees which has been found useful for enginesdriving rotary sickle type lawn mowers, washing machines, chain saws,lighting plants and all loads where the engine operates at governedspeed. In such cases, the advanced position of firing is chosen to fallwhere power output will be greatest at rated operating speed. In theretarded position the engine will then have easy starting free ofbackfiring and will idle more smoothly. It is to :be understood thatwhenever an engine equipped with the apparatus of this invention isslowed or brought to a stop, deceleration cannot'possibly beinstantaneous, due to the inertia of the moving engine parts and theinertia of the load. As a result, the cam 21 with its very small inertiawill be retarded in exery case of stopping or even of slowing down belowthe determined speed of advance. Therefore the engine will always beprepared for starting or will immediately assume retarded position foridling or improved lugging as soon as the engine is sufliciently slowed.

All of the above is accomplished by means which are extremely compactand, therefore, easily accommodated within a small engine magneto orbreaker with no significant change of dimension. The cost is,furthermore, but a small fraction of the value of the gain in enginerating which it permits, or of the saving in wear and tear upon pullstarters if the engine 'is prone to backfire on starting.

It is to be fully understood that the improvement of this inventionoperates to control the ignition primary circuit and is, therefore,equally adapted for use in connection with so-called battery systems. Insuch cases, the only modification required is that the cam and advancingmeans, herein shown and described, be substituted for the cam otherwiseemployed therein to drive the breaker contacts.

Where the apparatus of this invention is employed, in connection withmagneto ignition, it is preferred that the magneto employed exhibit wideor flat peak voltage characteristics, with the peak embracing the zoneof advance as nearly as possible. Where such is not possible, for easeof starting, it is preferred that the retarded position of firing shouldbe located favorably with respect to the peak of the magneto output.After full speed running is attained, the advanced position of firingneed not coincide with the maximum of the voltage peak since voltagewill be adequate on account of increased magneto speed.

The apparatus of this invention has been herein shown in use inconnection with a single cylinder engine but it will be obvious that itis adaptable for use with multiple cylinded engines as well.

The omission of a governor spring or other continuously acting biasingforce permits the use, in accordance with this invention, of a verysmall fly weight as compared with counterloaded governors in which theactuating force must be a small fraction only of the total centrifugalforce developed. This is particularly true in small high speed engines,because the high frequency vibrations prevailing which prevent theoccurrence of erratic friction between the cam 21 and the shaftextension 24 I claim:

1. In an ignition-timing advance mechanism for an internal combustionengine, having a breaker arm carrying breaker contacts, the combinationcomprising: a shaft adapted to be driven by said engine; a cam foractuating said breaker arm, said cam being mounted on said shaft forrotation therewith and for limited rotational displacement with respectthereto; friction means, including said breaker arm, engaging said camand thereby subjecting said cam to the frictional drag of said frictionmeans; a pivot, secured to said shaft in driven relation theretoadjacent one end of the cam; a fly weight pivotally secured to saidpivot and having a free end circumferentially spaced therefrom; and aconnection between the free end of said fly weight and said cam fordriving said cam and imparting an advancing torque thereto suflicient toovercome merely the frictional drag imposed on said cam by said frictionmeans when said shaft is driven at speeds in excess of idling speed.

2. Mechanism according to claim 1, wherein a split ring surrounds theshaft adjacent the cam, one part of the split ring being secured to theshaft to provide a mounting for the said pivot and the remaining portionof the said split ring being pivotally secured to said pivot to act asthe fly weight.

3. Mechanism according to claim 2, wherein the first part of the splitring provides stop means limiting the advancement of the cam by the flyweight.

4. Mechanism according to claim 1, wherein the pivot is mounted close tothe outer circumference of the shaft, and the fly weight extendsapproximately one-half the circumference of said shaft to its point ofconnection with said cam.

5. Mechanism according to claim 1, wherein an axially extending pivotextending between the free end of said fly weight and said cam forms theconnection therebetween.

6. In an ignition-timing advance mechanism for an internal combustionengine, having a moveable contact support for an electrical contactactive when moved to initiate the igniting spark for said engine, thecombination comprising: a shaft adapted to be driven by said engine intimed relation thereto; a cam for moving said contact support, said cambeing mounted on said shaft for rotation therewith and for limitedrotational displacement with respect thereto; friction means, includingsaid contact support, engaging said cam and thereby subjecting said camto the frictional drag of said friction means; centrifugal means, drivenby said shaft, and interposed between said shaft and said cam to imposeon the latter a centrifugally developed advancing torque, sufficient atspeeds above idling speeds, to overcome merely the frictional drag ofsaid friction means, and thereby to advance said cam, but limited in itscentrifugally developed advancing torque, at idling speeds to a valueless than said frictional drag.

7. Mechanism according to claim 6, wherein there is stop means carriedby the shaft, to limit the advancement of the cam.

8. In an ignition-timing advance mechanism for an internal combustionengine, the combination comprising: a rotatable member adapted to berotated by said engine; contact means for opening and closing theignition circuit; means for actuating said contact means, said actuatingmeans being mounted for rotating with the rotatable member in eitherretarded or advanced fixed relation thereto; stop means delimiting saidtwo fixed relations; friction means applied to the actuating means, forbiasing the latter to assume its retarded relation; and centrifugalmeans, carried by the rotatable member for biasing the actuating meansto assume its advanced relation, the biasing torque of the centrifugalmeans increasing with the angular velocity of the rotatable member, sothat this torque is less than the biasing torque of the friction meansat idle engine speeds, and is more than said biasing torque of thefriction means at working engine speeds; said two torques constitutingthe only imposed torques determinative of the angular relation of theactuating means to the rotatable member.

9. In an ignition-timing advance mechanism for an internal combustionengine, the combination comprising: a fixed support; a shaft rotatablewith respect to the support and adapted to be rotated by said engine;contact means for opening and closing the ignition circuit; means foractuating the contact means, said actuating means being mounted forrotation with the shaft, and movable with respect to the shaft withinlimits defining an advanced and a retarded position; friction meansmounted on the support, and engaging the actuating means to applythereto a torque biasing the actuating means to move toward retardedposition when the actuating means is rotating; and centrifugal means,mounted on the shaft and engaging the actuating means, to apply theretoa torque biasing the actuating means to move toward advanced positionwhen the shaft is rotating; the biasing torque of the centrifugal meansincreasing with the angular velocity of the shaft so that this torque isless than the biasing torque of the friction means at idle enginespeeds, and is more than the biasing torque of the friction means atworking engine speeds; the centrifugal means constituting the onlymeans, mounted on the shaft and engaging the actuating means, to apply abiasing torque to said actuating means.

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